Party build advice

I may be opening a pandora's box here, but i wanted to get some tips and ideas on my party build, and see if I'm doing anything wrong.

I'm not a min/maxer, and a lot of times i feel like i'm missing crucial system behavior.

First my character:

Wizard (no subclass) / Cipher (beguiler)

Took no wiz subclass because the penalties seem to out way the bonuses by way too much. I use a lot of CC spells, some dmg.

Cipher - took beguiler for the buff in the deception abilities for a lot of CC. But I may have misunderstood the whole sneak attack thing? What does sneak attack vulnerable means? Only when I'm hidden? then in full combat its useless?

Eder - full fighter. Tank, sword and shield

Aloth - Battlemage. Thought it might be fun to play a melee wizard that buffs himself. Using him with dual wielding. Any tips for his build as well i'd appreciate

Xoti - full priest

Serafen  - Barbarian/Cipher (Witch) using dual wielding firearms(currently his starting pistol and blunderbuss)

Now im interested in Pallegina as well to take as Paladin/Chanter when i get the change, but i can't think of who i would replace her with...difficult choice....